The major objective of this work is to isolate, purify and determine the structure of the antitumor alkaloids present in Catharanthus roseus, Catharanthus trichophyllus and Rhazya stricta. The Malagasy plant Catharanthus roseus is a well established source of antitumor agents of the dimeric indole alkaloid class. However several highly active fractions remain to be studied for their constituents. The crude alkaloid mixtures will be separated initially by pH gradient techniques and subsequently by column chromatography; monitoring each step with an appropriate biological assay technique. Isolated compounds will be identified by their mp, mass UV and IR spectra, optical rotation CD and PMR spectra. Structure elucidation will be carried out by interpretation of these data, chemical correlation with known compounds and in particularly difficult cases by single crystal X-ray crystallography.